reverse lambda expression

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I am trying to find a way to examine the expression passed into a function.

assuming I make this call

DoIt( ()=>new Person().FirstName );

to

public static string DoIt<t> (Func<t> callme){
   return "what did callme point to";
}
</t></t>

Is is possible for DoIt to return "FirstName"? and if so can you point me in the right direction please?

Many thanks.

Posted 5-Apr-11 7:58am

cechode

Updated 6-Nov-16 14:14pm

v3

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Comments

wizardzz 5-Apr-11 14:03pm

Fixed typo.

Sander Rossel 5-Apr-11 14:35pm

You actually missed the big typo in the subject!
http://en.wikipedia.org/wiki/Lambada :D

wizardzz 5-Apr-11 14:40pm

Haha, I must have been thinking of this:
http://www.youtube.com/watch?v=PK2HANwsUWg

Sander Rossel 5-Apr-11 14:43pm

Brings back memories :)
If LaBamba Then
SomeLameJokes
End If
:D

cechode 5-Apr-11 15:00pm

LOL thx, not sure what i was thinking about ( heh)
actually i'm just a horrible speller :)
thx

3 solutions

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Sergey Alexandrovich Kryukov · Answer 1 · 2011-04-05T08:05:00

Solution 1

Sorry if I don't understand your idea fully, but did you pay attention for System.Delegate.GetInvocationList? It answers exactly the question "what did callme points to". This is nothing like "reverse lambda" though.

Maybe you need to explain your vaguely expressed idea in terms what you want to achieve, exactly, and what would be the ultimate purpose of it…

[EDIT]
Answering the follow-up question/clarification.
This is about Expressions and Expression Trees. Please see http://msdn.microsoft.com/en-us/library/bb397951.aspx[^].

—SA

Posted 5-Apr-11 8:05am

Sergey Alexandrovich Kryukov

Updated 5-Apr-11 9:19am

v2

Comments

cechode 5-Apr-11 15:03pm

GetInvocationList does not return the desierd information!
the usage is simple. Do something based on either the name of the last member in the tree or a value of an attribute that might exist on that ;ast member. ( FirstName in the exampe above )

Sergey Alexandrovich Kryukov 5-Apr-11 15:53pm

Please see my update and our discussion with dasblinkenlight. I think all you can do is to work along these lines.

My I ask you how do you see your ultimate purpose?

To give you an idea: I developed a fully-fledged technology for Computer Algebra System. The latest and most advanced implementation was C#, and it was before Expression trees. I've done the expression trees from scratch, which has serious benefits (except compatibility with v.2.0 :-). I also can work as both symbolic and digital calculator.

Do you aim to develop something like that?

--SA

dasblinkenlight · Answer 2 · 2011-04-05T08:51:00

Solution 2

This is a hard problem - you need a decompiler to do it. There is a hint of the solution[^] that you can use as a template, but it involves a lot of coding.

Posted 5-Apr-11 8:51am

dasblinkenlight

Comments

Sergey Alexandrovich Kryukov 5-Apr-11 15:20pm

I think this is just about Expression Trees. Please see my update to my Answer (after [EDIT]).
--SA

dasblinkenlight 5-Apr-11 15:30pm

From his example it looks like he's not dealing with expression trees, because he gets Func[t] as an argument.

Sergey Alexandrovich Kryukov 5-Apr-11 15:33pm

I see. Nevertheless, the intent is using expression tree, I think.
--SA

dasblinkenlight 5-Apr-11 15:39pm

Yeah, that's very much the only option there is. The question is, how do you get one if all you've got is a compiled function. The guy at my link suggests decompiling into an expression tree. It would be a lot simpler if the OP could use an expression tree instead, because the code could both examine the tree and produce an executable expression by calling Compile().

Sergey Alexandrovich Kryukov 5-Apr-11 15:43pm

I think you're right.
--SA

cechode 5-Apr-11 15:55pm

now this is what i call a GOOD DAY !
thank you guys, between the Expression path and the ExpressionVisitor path i have learned alot today!!!

( also learned that just because you can does not mean you should :) )

thx again all .

Member 2862495 · Answer 3 · 2016-11-06T14:14:00

Solution 3

C#

var actual0 = value.Aggregate(new StringBuilder(), (x, y) => x.Insert(0, y)).ToString();

Posted 6-Nov-16 14:14pm

Member 2862495

Comments

CHill60 12-Nov-16 21:26pm

In what way does this answer the 5 year old question?

reverse lambda expression

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